1. Field of the Invention
The invention relates to a method and an apparatus for generating plasma pulses that can be used for high-precision three-dimensional plasma treatment in particular.
2. Description of Related Art
There is a wide variety of low-temperature plasma applications in a multitude of different configurations in the low-pressure range or at atmospheric pressure, wherein an ever-recurring problem consists in obtaining a desired spatial distribution or uniformity of the plasma or the products thereof. In particular, this problem occurs when large-surface workpieces or three-dimensional shapes are to be treated.
A method for the focusing of microwaves in a spatial position in the field of medicine is known from Publication No. WO 2006/119379 A1. According to that method, an antenna radiates a microwave toward the region to be treated. The signals reflected from said region are received by further antennas of an antenna array and analyzed by an analyzing unit. For the purpose of treating said region, the time-inverted microwaves are radiated by the antenna array. A disadvantage of that solution consists in the fact that it is only suitable for the treatment of static regions.
Furthermore, in the field related to the present invention, a power supply device for bipolar power supply is known from German Published Patent Application No. DE 100 18 879 A1. The power supply device comprises two switching units, by means of which output pulses having a predeterminable amplitude, having a predeterminable pulse duration and having a predeterminable interval between pulses can be generated. DE 100 18 879 A1 does not describe any superposition of the output pulses for generating a predeterminable local field strength. Rather, a geometrical development of the plasma is achieved by a special arrangement of the electrodes.
A circuit arrangement for a power supply device for devices and plants for plasma technology and surface engineering is described in Utility Model No. DE 92 10 382 U1. The distribution of the plasma is optimized by controlling the output pulses. DE 92 10 382 U1 is about an extensive volume plasma but not about local plasma excitation.
U.S. Pat. No. 5,932,116 A relates to a power supply for pulse output by several electrodes. According to that publication, the electrodes are activated sequentially and do not jointly act on a local point of treatment.
European Patent Specification No. EP 0 674 369 B1 relates to a gas laser with microwave excitation, wherein a gas medium is excited by a multitude of microwaves in such a manner that it reaches a high energy state, wherein the directions of the oscillations of the electric field of the microwaves differ from each other. Furthermore, the microwaves have pulse microwaves synchronized by the gas laser.
A device for the generation of microwave plasma is disclosed in European Patent Application No. EP 0 503 082 A1. The device radiates microwaves into a discharge space in order to generate plasma in a wide area in fixed positions and over a long period of time. To this end, microwave pulses are continuously outputted at various time intervals by a multitude of microwave transmitters.